Physical Methods for Heavy Metal Wastewater Treatment

The methods for treating Heavy Metal Wastewater can be roughly divided into:

• Chemical methods
• Physical method
• Biological method

Chemical Methods mainly include chemical precipitation and electrolysis, which are mainly suitable for the treatment of wastewater containing high concentrations of heavy metal ions.

Physical Methods mainly include solvent extraction separation, ion exchange method, membrane separation technology, and adsorption method.

Solvent Extraction Separation

Solvent extraction is a commonly used method for separating and purifying substances. When using this method, it is necessary to choose extractants with high selectivity.

Heavy metals in wastewater generally exist in the form of cations or anions. For example, under acidic conditions, they undergo complex reactions with extractants, are extracted from the aqueous phase to the organic phase, and then re extracted to the aqueous phase under alkaline conditions, allowing the solvent to be regenerated for recycling. This requires careful selection of aqueous acidity during extraction operations.

Feature:Liquid-liquid contact, continuous operation is possible and the separation effect is good.Although the extraction method has significant advantages, the loss of solvents during the extraction process and the high energy consumption during the regeneration process make this method have certain limitations and its application is greatly limited.

Ion Exchange Method

Ion exchange method is a method of exchanging heavy metal ions with ion exchangers to remove heavy metal ions from wastewater.

Commonly used ion exchangers include cation exchange resins, anion exchange resins, chelating resins, etc. With the continuous emergence of ion exchange agents, ion exchange methods have increasingly demonstrated their advantages in the advanced treatment of electroplating wastewater and the recovery of high-value metal salts.

Feature: Ion exchange method is an important electroplating wastewater treatment method with large treatment capacity, good effluent quality, recyclable heavy metal resources, and no secondary pollution to the environment. However, ion exchange agents are prone to oxidation failure, frequent regeneration, and high operating costs.

Membrane Separation Technology

Membrane separation technology is a method of separating or concentrating solvent and solute by using a special semi permeable membrane under the effect of external pressure without changing the chemical form in the solution, including electrodialysis and diaphragm electrolysis.

• Electrodialysis is a physical chemical process in which heavy metal ions in aqueous solution are separated from water by using anion and cation exchange membrane to selectively penetrate anion and cation of solution under the action of DC electric field.
• Diaphragm electrolysis is a method of electrolysis by separating the anode and cathode of the electrolysis device with a membrane. In fact, it is a combination of electrodialysis and electrolysis.

Feature: The above methods have encountered issues such as electrode polarization, scaling, and corrosion during operation.

Adsorption Method

Adsorption method is an effective method for removing heavy metal ions from water by utilizing porous solid substances for adsorption.

The key technology of adsorption method is the selection of adsorbent. The traditional adsorbent is activated carbon, as well as clay adsorbent powder, coal ash adsorbent, biomass based materials, and resin based adsorbent materials.

Feature:  Activated carbon has strong adsorption capacity and high removal rate, but its regeneration efficiency is low, making it difficult to meet the reuse requirements for water treatment. Its price is expensive and its application is limited.

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